Toyota explains hot hydrogen tech advantages

TOYOTA Australia has announced its position as a key player in the development of hot hydrogen – or hydrogen internal combustion – technology for a future range of larger SUVs, four-wheel drives and utility vehicles, beginning with the HiAce Commuter bus.

Under Toyota’s stated multi-pronged strategy to lower CO2 emissions across its fleet, the Japanese giant is investing in a range of driveline technologies including fuel cell hydrogen, hydrogen internal combustion, battery electric, hybrid, and cleaner-burning internal combustion engines with and without mild hybrid assistance.

But it is the benefits to not only the planet, but also Toyota’s bottom line, that form an interesting part of the hot hydrogen push.

Development and tooling costs associated with hydrogen internal combustion engines are virtually nil, the changeover from petrol to hydrogen being relatively straightforward and applicable to both naturally aspirated and forced induction engines with little modification.

In addition, the thermal efficiency of a spark ignition hot hydrogen engine is similar to that of a compression ignition diesel unit.

Hot hydrogen can be applied in a hybridised arrangement to leverage existing electrification technology, a bonus for Toyota as the world’s largest producer of hybrid drivetrains.

The absence of carbon means almost no CO2 (carbon dioxide), CO (carbon monoxide) or HC (hydrocarbon) emissions are produced from a hot hydrogen engine.

However, harmful oxides of nitrogen (NOx) emissions can be high when hot hydrogen engines are tuned to deliver equivalent performance to the petrol units on which they are based.

Once NOx emissions are addressed – Toyota is working on this – hot hydrogen can yield extensive supply chain, research and development, and manufacturing cost advantages.

These are in addition to the environmental benefits associated with hydrogen combustion – provided sufficient quantities of this fuel can be sustainably produced without a carbon footprint or causing other ecological harm.

Understanding the technology

Toyota has extensive experience in hydrogen fuel cell electric vehicle (FCEV) technology, with memorable past examples including the RAV4 (1996), Kluger (2001), Fine series concepts (2003-05), and FCV-R (2011) and FCV concepts, which eventually became the Mirai FCEV now available in its second generation in selected markets.

There is even a HiLux hydrogen FCEV prototype doing the rounds in the UK, running on a modified version of the Mirai’s powertrain.

But it is important to understand the differences between FCEV technology, where a fuel cell uses hydrogen electrochemically to produce electricity (cold hydrogen), and internal combustion (hot hydrogen) technology as demonstrated in the HiAce Commuter H2.

Hot hydrogen uses an internal combustion (spark ignition) engine converted to run on hydrogen instead of petrol. It is a surprisingly old technology that has been tried by several manufacturers back as far as 1806  and one that improves the thermal efficiency of a spark ignition petrol engine to levels approaching that of a compression ignition diesel engine.

According to Toyota Powertrain and Commercial Vehicle chief engineer Takaaki Nakazono, Toyota is working to achieve similar outputs from the HiAce Commuter’s hydrogen combustion engine as those developed by the 305kW/650Nm V35A-series petrol on which it is based.

Mr Nakazono was one of the lead engineers tasked with development of the 3.5-litre V35A-FTS engine – found under the bonnet of the LandCruiser 300 Series and others in overseas markets – and is currently developing hydrogen combustion technology for use in this application, and others.

He explained that at the present time, the H2-ICE arrangement allows an output of only 120kW and 354Nm while meeting emissions standards.

However, Mr Nakazono says exhaust technology currently under development will allow a richer fuel/air mixture to extract power and torque figures closer to those of the twin-turbocharged petrol – an additional 185kW and 296Nm – in the very near future, all while maintaining the hydrogen unit’s superior thermal efficiency statistics.

“The thermal efficiency levels of the combustion hydrogen engine are very similar to those of a diesel engine,” Mr Nakazono told GoAuto.

“If we compare a Mirai FCEV and the HiAce hydrogen engine and considering the size of the FCEV units and the size of the combustion engine, when producing around 90 kilowatts or more of energy, the thermal efficiency between the FCEV and the hydrogen combustion engine will switch.”

Mr Nakazono’s Australian colleague and senior manager of vehicle evaluations and regulations for Toyota Australia, Ray Munday, said it was important to note that efficiency under load was a critical benefit of H2-ICE technology, underlining the importance in delivering diesel-like drivability from the HiAce Commuter H2 prototype.

“Efficiency under load is a critical point. With electric motors and other points (within the FCEV driveline) as you load them more, their efficiency drops. That’s why with hydrogen combustion technology, in heavy loading scenarios, there is an efficiency advantage,” he stated.

According to an article published by Australian-founded publication The Conversation, only 38 per cent of the energy used to produce green hydrogen ends up turning the wheels of an FCEV. 

Conversely, 80 per cent of the energy generated to charge a BEV ends up turning the wheels. Further, petrol internal combustion engines are at best 38 per cent thermally efficient and diesel internal combustion engines 42 per cent.

The thermal efficiency of H2-ICE engines is much the same as their diesel counterparts.

Detailing the rationale behind the lower output figures of the early prototype, Mr Nakazono said that exhaust controls, and not engine technology, is the current sticking point of the technology.

“There are two options (to producing more power and torque). One is to simply make the displacement of the engine bigger,” he continued.

“Currently, to comply with emissions regulations, the combustion is a lean burn. With a lean burn system, together with the SCR (exhaust) system that is used for the diesel engine we can meet emissions regulations. But to further increase output using the current engine – and meet emissions standards – a new style of emissions control would need to be developed.

“We are already developing such a system, and in the future, there is the potential that we can produce a hydrogen combustion engine with similar outputs to a petrol combustion engine, and while maintaining emissions regulations.”

But can H2-ICE technology outpace FCEVs and BEVs?

As for competitor technologies, and especially those being developed by Toyota and others in the battery electric field, Mr Nakazono says the hydrogen option is set to still win out, at least in certain applications.

He believes that in regional areas of developed countries, in countries without abundant access to renewable electricity and appropriate charging infrastructure, and in larger vehicle applications, hydrogen combustion technology very much has its place.

“Even when we see renewable electricity become far more abundant than it is today, I believe that in rural areas, and regions outside of the metropolitan zones, hydrogen is a good option,” he said.

“And even when electricity is produced from renewables, there is a kind of peak of when electricity can be generated, which means it is necessary to store this energy for other times. It is here we believe hydrogen is a very good option.”

Concurring with Mr Nakazono, Toyota Australia’s Ray Munday told GoAuto it was important that electric vehicles were not seen as the answer to the decarbonisation of vehicle fleets in every scenario.

“This is not just an Australian development, but one that will reach around the world. We see that each country is developing efficiencies (in renewable energy production) at different rates. We also see a growing demand for faster refill times, especially in heavier usage applications. In both cases, hydrogen has an advantage (over grid-sourced electricity),” he explained.

“For these types of consumers, this is where we need to be right now. With current battery technology, that’s an issue we can’t address. And of course, this is changing, it is changing all the time.

“The cost of hydrogen production is coming down, and obviously that is part of the Australian government’s national hydrogen strategy, it is for us (Australia) to be a leader on a world scale.”

Interestingly, Toyota chief technology officer, Hiroki Nakajima, told journalists at the recent Japan Mobility Show (Tokyo Motor Show) that one of the failings of the Mirai was that hydrogen refuelling stations are few and far between.

But as he sees it, the technology has a brighter future in applications such as the HiAce, and in the commercial sector more broadly.

“We have tried Mirai but have not been successful. Hydrogen stations are very few and difficult to realise (without greater support for development of the required infrastructure). This is why the Mirai sells only in small volumes,” he said.

“For mid-size trucks, it is easier to deliver a refuelling network as the vehicles are used mainly for A-to-B type journeys. Huge numbers of trucks go from A-to-B, so you can operate stations with more stability.

“Commercial vehicles are the most important area to try and proceed with hydrogen,” he emphasised.

According to US publication Hydrogen Insight, Mr Nakajima said Toyota would continue to research and develop hydrogen fuel cell technology for use in cars, but believed it was important to also develop more compact hydrogen fuel tanks and fuel cells that would fit in a wider range of vehicles.